How To Run Ubuntu 15.04 Screen on Samsung Galaxy2

I'm sure that many of us (Android Fans) have somewhere in house an (unused or not so used) Samsung Galaxy Tablet. The good news is that we can use this device as a second display for Ubuntu screens. Is not that feeling when using a second real Display/Monitor having 21.5" inch or bigger because these tiny tablets are having only 12.2" Zoll/inch. But still, the maximum size of Galaxy can be adapted to 1280x768 pixels and is quite good. Disadvantages are two: Galaxy battery has to be charged because not everytime the battery charging works using USB from Notebook. Second disadvantage is that is impossible to drag the Screens from VNC Session to Ubuntu and Back. Screen control has to be made using VNC Viewer.